• Current Optics and Photonics
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• 제3권5호
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• pp.438-444
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• 2019

In this theoretical study, a line-defect photonic-crystal waveguide hosted in an annular photonic crystal was demonstrated to provide high-performance slow light with a wide band, low group-velocity dispersion, and a large normalized delay-bandwidth product. Combined with structural-parameter optimization and selective optofluid injection, the normalized delay-bandwidth product could be enhanced to a large value of 0.502 with a wide bandwidth of 58.4 nm in the optical-communication window, for a silicon-on-insulator structure. In addition, the group-velocity dispersion is on the order of $10^5$ ($ps^2/km$) in the slow-light region, which could be neglected while keeping the signal transmission unchanged.

• Current Optics and Photonics
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• 제1권1호
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• pp.60-64
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• 2017

We have considered optical nonlinearities of coupled quantum dots theoretically, where an exciton dipole-dipole interaction is mediated between the adjacent large and small quantum dots. For increasing a pump pulse area in resonance with the large quantum dot exciton the induced nonlinear refractive index of the small quantum dot exciton has been obtained. As the exciton dipole-dipole interaction depends on the relative orientation of two exciton dipoles, the optical nonlinearities for the directions parallel and perpendicular to the coupling axis of the two quantum dots are compared. The directional imbalance of optical nonlinearities in coupled quantum dots can be utilized for a polarization phase modulator by controlling a pump pulse area and propagation length.

• Current Optics and Photonics
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• 제5권6호
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• pp.730-737
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• 2021

Transmission spectra are measured from waveguide-coupled ring resonators fabricated with SiN_x on SiO₂. By using ring resonators with various radii and several index contrasts, the behavior of the quality factors is investigated. As the index contrast decreases, the dominant loss is from scattering for a large resonator, while that changes from scattering loss to bending loss for a small resonator. We verify that the quality factor can be drastically improved by reducing the index contrast in large ring resonators.

• Journal of electromagnetic engineering and science
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• 제8권3호
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• pp.100-109
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• 2008

The finite volume time domain(FVTD) technique faces serious limitations in simulating electromagnetic scattering at high frequencies due to requirements related to discretization. A modified FVTD method is proposed for electrically large, perfectly conducting scatterers by partially incorporating a time-domain physical optics(PO) approximation for the surface current. Dominant specular returns in the modified FVTD method are modeled using a PO approximation of the surface current allowing for a much coarser discretization at high electrical sizes compared to the original FVTD scheme. This coarse discretization can be based on the minimum surface resolution required for a satisfactory numerical evaluation of the PO integral for the scattered far-field. Non-uniform discretization and spatial accuracy can also be used in the context of the modified FVTD method. The modified FVTD method is aimed at simulating electromagnetic scattering from geometries containing long smooth illuminated sections with respect to the incident wave. The computational efficiency of the modified FVTD method for higher electrical sizes are shown by solving two-dimensional test cases involving electromagnetic scattering from a circular cylinder and a symmetric airfoil.

• 한국정밀공학회지
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• 제33권6호
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• pp.491-497
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• 2016

This study aims to develop a vision inspection system for screw threads. To inspect external defects in screw threads, the vision inspection system was developed using front light illumination from which bright images can be obtained. The front light system, however, requires multiple side images for inspection of the entire thread surface, which can be performed by omnidirectional optics. In this study, an omnidirectional optical system was designed to obtain annular images of screw threads using an image sensor and two reflection mirrors; one large concave mirror and one small convex mirror. Optical simulations using backward and forward ray tracing were performed to determine the dimensional parameters of the proposed optical system, so that an annular image of the screw threads could be obtained with high quality and resolution. Microscale surface defects on the screw threads could be successfully detected using the developed annular inspection system.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.741-744
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• 2005

A numerical scattering model for artificial metal structure based on physical optics approximation is developed to identify the height of phase center, and the result is compared with interferometric SAR DEM. The interferometric SAR data were gathered by AIRSAR during PACRIM- II campaign on Jeju Island. Power transmission towers on piedmont pasture along the slopes of Mt. Halla look like elliptic risings in TOPSAR DEM. The heights of risings are quantitatively analyzed using a scattering model in the way of achieving the height of phase centers of power transmission towers. A numerical algorithm is developed on the basis of physical optics approximation. The structure of power transmission tower was decomposed into hundreds of rectangular metal plates, of which the scattering matrix is known in analytic form, and the calculated scattering fields were summed coherently. The effect of direct backscattering component, ground-scatterer component and scatterer-ground component are decomposed and computed individually for each rectangular metal plate. The $\Deltak-radar$ equivalent was used to calculate height of phase center of the scatterer. The heights of a selected power transmission tower and scattering algorithm results give existence and location of the transmission towers but not actual tower heights.

• 한국안광학회지
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• 제16권2호
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• pp.97-105
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• 2011

목적: 본 연구는 한국의 안경광학 분야에서 사이버콘드리아 현상의 실태를 파악하고 그에 대한 적절한 대책을 제시하는 것을 목적으로 실시되었다. 방법: 일반소비자 집단과 현역안경사 집단을 대상으로 사이버콘드리아 현상과 관련된 설문조사를 실시하고, 그 결과를 분석하였다. 결과: 한국의 안경광학 분야에서 온라인 정보에 대한 인식에 있어 일반소비자 집단과 안경사 집단 사이에 괴리가 크게 나타나면서 사이버콘드리아 현상이 존재함을 알 수 있었다. 결론: 사이버콘드리아에 대한 대책으로는 안경사의 적극적인 상담이 가장 적절하고 효과적인 것으로 판단된다.

• 한국광학회지
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• 제13권2호
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• pp.155-161
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• 2002

혼탁매질인 손톱의 하부면에는 개인별로 상이한 융선과 곡 구조의 패턴인 조상(爪床, nail bed)이 있다. 이중 융선에는 혈액이 흐르는 모세혈관 고리(capillary loop)가 밀집되 있고 융선과 융선은 모세혈관 고리가 밀집되 있지 않은 골로 구분되어 있다. 670nm 파장의 레이저 빛은 피부의 진피(dermis)에서 산란특성을 가지며 혈액에는 강하게 흡수된다. 손톱하부면 조상(nail bed)의 이와 같은 생체-광학적 특성에 착안하여 혼파매질인 손톱하부면에 위치하는 조상(nail bed) 패턴을 얻어내는 콘포칼 광 스케닝(confocal optical scanning) 구조를 특징으로 하는 광학계를 제안한다. 그리고 이를 이용하여 개인별로 상이한 조상(nail bed) 패턴을 추출해 조상(nail bed) 패턴간의 correlation를 구해 비교함으로써 개인을 구별해내는 개인인증 기법을 제안한다.

• Journal of the Optical Society of Korea
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• 제19권5호
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• pp.449-455
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• 2015

In this study we propose a new photonic crystal fiber (PCF) design that simultaneously offers broadband single-mode operation, high birefringence, and large normal dispersion in the optical-communication wavelength regime. The waveguide is based on a hybrid square-lattice PCF (HS-PCF) that has circular air holes of two different diameters alternating in the cladding, plus a pure silica defect at the center. The optical properties of the guided modes are analyzed numerically by the finite-element method (FEM) with a perfectly matched layer as the boundary condition. The optimized HS-PCF has a dispersion coefficient of $-601.67\;ps\;nm^{-1}\;km^{-1}$ and a high birefringence of $1.025{\times}10^{-2}$ at $1.55{\mu}m$. In addition, over the S+C+L+U wavelength bands the proposed HS-PCF with ultraflat birefringence with a slope on the order of $10^{-5}$.

• 대한조선학회논문집
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• 제45권6호
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• pp.695-702
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• 2008

In this paper, a new numerical method is proposed to analyze near-field sonar cross section of acoustically large-sized underwater targets such as submarines. A near-field problem is converted to a far-field problem using a spherical projection method with respect to the objective target. Then, sonar cross section is calculated with a physical optics well established in far-field acoustic wave scattering problems. The analysis results of a square flat plate compared with those obtained by other method show the accuracy of the proposed method. Moreover, it is noted that the sonar cross section is varied with respect to the targeting point as well as the range. Finally, numerical analysis results of real-like underwater target such as a submarine pressure hull are discussed.